This research plan describes the development of a new technology using state-of-the-art silicon microelectronics fabrication techniques to produce multiplexed electrode arrays. Ongoing work in the area of cardiac cell culture studies has demonstrated the feasibility of studying spatio-temporal processes in cell cultures using microelectrode array. These arrays are limited by the number of electrical contacts to the cultures. In order to perform detailed studies of the electrical activity of cardiac cell cultures, a 16 x 16 mutiplexed electrode array is proposed. The proposed electrode array requires a new technology of passivated microelectronics which can function in saline environments. High temperature silicon nitride passivation will be used to protect the devices. A high temperature metallization system which is compatible with the silicon nitride depositions will be used as interconnect. N-channel MOS devices will be placed at 1mm. intervals in a 16 x 16 array. The gates of the devices will contact the cell culture via 10 x 10 micron contacts. The sources will be connected along 16 buses. The drains will be connected along 16 other buses. By selecting the appropriate source and drain, a specific device can be selected for recording. By scanning the devices at a clock frequency of 750 kHz, it will be possible to sample each electrode at about 3 kHz. This will effectively produce simultaneous recordings from the 256 electrodes in the culture. The devices will be electrically tested and will also be tested for function in the saline environment of the cardiac cell cultures. This technology, if successful, will provide the basis for extensive cardiac and neural cell culture studies, and will provide an increment in progress towards the development of implantable devices which will survive the saline environment for decades.